Shigella spp. are obligate intracellular pathogens and causative agents of shigellosis (a form of bacillary dysentery) that causes an estimated 1.1 million deaths worldwide per annum. Furthermore, Shigella has been cited as a Type B agent of bioterrorism. The pathogenesis of Shigella involves the invasion of colonic epithelial cells. Once the bacteria have entered a cell they replicate and recruit actin filaments for directional movement within these cells and for subsequent invasion of adjacent cells. The Shigella outer membrane protein, IcsA is essential to Shigella pathogenesis in that this is the sole bacterial protein required for the recruitment of actin filaments. IcsA is expressed on a large 220- kilobase virulence plasmid found in all species of Shigella. Furthermore, IcsA is unique in that it is targeted and restricted to the old pole of the bacterium. Preliminary studies indicate that the asymmetrical distribution of IcsA is directly correlated with directional movement of Shigella within colonic epithelial cells and its efficient dissemination to uninfected cells. Therefore an understanding of the mechanisms by which IcsA is expressed, targeted to the old pole of the bacillus, secreted and maintained at the pole is important in addressing the pathogenic nature of Shigella. Experiments proposed in this application involve the identification and analysis of a chromosomal gene that globally regulates the expression of icsA and the identification of proteins that define a putative polar receptor for the IcsA. PUBLIC HEALTH RELEVANCE: The goals stated in the proposal are to identify and analyze chromosomal genes that globally regulate the expression of icsA and that define a putative polar receptor for the IcsA protein. Successful completion of the goals stated above should aid in better understanding how Shigella respond to the environment to activate virulence factors and how IcsA is targeted to a location in an individual bacterium such that the bacteria can most efficiently spread from one colonic epithelial cell to adjacent cells. Such understanding should lead to the development of therapeutic drugs or vaccines that can disrupt these processes.